DOCSIS is a protocol that is used to send digital video and data between a hub or headend facility (HEF), and a cable modem (CM) and/or a set-top box at a customer premise. Motion Picture Experts Group (MPEG)-transport stream (TS) based digital video is generally a one-way or downstream application from the head-end to the set-top box. Internet protocol (IP) based video streams today are also predominantly from the head end to the set-top box. However, IP video streams may also be sent from the home environment to the head-end, i.e., IP video may be sent upstream.
Control information for a legacy MPEG-TS stream can be both one-way and two-way, e.g., downstream or both downstream and upstream. For basic video services, a single downstream broadcast control channel is sufficient. For many legacy set-top boxes, the control channel consists of an out-of-band (OOB) carrier located at or near 75 MHz in the downstream spectrum.
For downstream and upstream transport, the digital data are modulated onto a Radio Frequency (RF) carrier or channel using Quadrature Amplitude Modulation (QAM) techniques. DOCSIS version 3.0 expands DOCSIS capability beyond a single RF carrier to multiple RF carriers using a technique known as channel bonding in order to reduce latency and/or to increase the capacity or traffic burst capability for a particular service flow. Channel bonding essentially uses packet multiplexing across two or more RF carriers.
As users begin to send more data upstream, e.g., by exchanging photographs or movies, increased demands are placed on the upstream bandwidth. Cable system operators have been looking for ways to increase upstream capacity. Part of the solution has been channel bonding as described above. However, legacy cable system components were not designed with the increasing demands of modern cable system end users for both upstream and downstream traffic.